4,532 research outputs found
Properties of the energy landscape of network models for covalent glasses
We investigate the energy landscape of two dimensional network models for
covalent glasses by means of the lid algorithm. For three different particle
densities and for a range of network sizes, we exhaustively analyse many
configuration space regions enclosing deep-lying energy minima. We extract the
local densities of states and of minima, and the number of states and minima
accessible below a certain energy barrier, the 'lid'. These quantities show on
average a close to exponential growth as a function of their respective
arguments. We calculate the configurational entropy for these pockets of states
and find that the excess specific heat exhibits a peak at a critical
temperature associated with the exponential growth in the local density of
states, a feature of the specific heat also observed in real glasses at the
glass transition.Comment: RevTeX, 19 pages, 7 figure
Diamagnetic Response of Normal-metal -- Superconductor Double Layers
The magnetic response of a proximity-coupled superconductor-normal metal
sandwich is studied within the framework of the quasiclassical theory. The
magnetization is evaluated for finite values of the applied magnetic field
(linear and nonlinear response) at arbitrary temperatures and is used to fit
recent experimental low-temperature data. The hysteretic behavior predicted
from a Ginzburg-Landau approach and observed in experiments is obtained within
the quasiclassical theory and shown to exist also outside the Ginzburg-Landau
region.Comment: RevTex, 11 pages, 9 PostScript figures include
Anomalous density of states of a Luttinger liquid in contact with a superconductor
We study the frequency and space dependence of the local tunneling density of
states of a Luttinger liquid (LL) which is connected to a superconductor. This
coupling {\em strongly} modifies the single-particle properties of the LL. It
significantly enhances the density of states near the Fermi level, whereas this
quantity vanishes as a power law for an isolated LL. The enhancement is due to
the interplay between electron-electron interactions and multiple
back-scattering processes of low-energy electrons at the interface between the
LL and the superconductor. This anomalous behavior extends over large distances
from the interface and may be detected by coupling normal probes to the system.Comment: 8 pages Revtex, two postscript figure
Charge Transport in Voltage-Biased Superconducting Single-Electron Transistors
Charge is transported through superconducting SSS single-electron transistors
at finite bias voltages by a combination of coherent Cooper-pair tunneling and
quasiparticle tunneling. At low transport voltages the effect of an ``odd''
quasiparticle in the island leads to a -periodic dependence of the current
on the gate charge. We evaluate the characteristic in the framework of a
model which accounts for these effects as well as for the influence of the
electromagnetic environment. The good agreement between our model calculation
and experimental results demonstrates the importance of coherent Cooper-pair
tunneling and parity effects.Comment: RevTeX, 12 pages, 4 figure
Phase diffusion and locking in single-qubit lasers
Motivated by recent experiments, which demonstrated lasing and cooling of the
electromagnetic field in an electrical resonator coupled to a superconducting
qubit, we study the phase coherence and diffusion of the system in the lasing
state. We also discuss phase locking and synchronization induced by an
additional {\sl ac} driving of the resonator. We extend earlier work to account
for the strong qubit-resonator coupling and to include the effects of
low-frequency qubit's noise. We show that the strong coupling may lead to a
double peak structure of the spectrum, while the shape and width are determined
to the low-frequency noise.Comment: Revised version with a new section about the validity of the model
when applied to describe experiment
Atomic cluster state build up with macroscopic heralding
We describe a measurement-based state preparation scheme for the efficient
build up of cluster states in atom-cavity systems. As in a recent proposal for
the generation of maximally entangled atom pairs [Metz et al., Phys. Rev. Lett.
97, 040503 (2006)], we use an electron shelving technique to avoid the
necessity for the detection of single photons. Instead, the successful fusion
of smaller into larger clusters is heralded by an easy-to-detect macroscopic
fluorescence signal. High fidelities are achieved even in the vicinity of the
bad cavity limit and are essentially independent of the concrete size of the
system parameters.Comment: 14 pages, 12 figures; minor changes, mainly clarification
Single-qubit lasing and cooling at the Rabi frequency
For a superconducting qubit driven to perform Rabi oscillations and coupled
to a slow electromagnetic or nano-mechanical oscillator we describe previously
unexplored quantum optics effects. When the Rabi frequency is tuned to
resonance with the oscillator the latter can be driven far from equilibrium.
Blue detuned driving leads to a population inversion in the qubit and a
bi-stability with lasing behavior of the oscillator; for red detuning the qubit
cools the oscillator. This behavior persists at the symmetry point where the
qubit-oscillator coupling is quadratic and decoherence effects are minimized.
There the system realizes a "single-atom-two-photon laser".Comment: Replaced with final published version, fig. 2 compresse
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